Understanding the H.248 Feature

The H.248 feature provides a gateway control interface between the PGW 2200 and the VXSM gateways. It supplements the MGCP protocol. This new interface is based on the ITU-SG16/IETF specification of H.248 which defines a decomposed gateway architecture.

This architecture is composed of

•A media gateway controller (MGC) and the media gateways (MGs)

•Distributed call control functionality between an MGC (an intelligent entity that manages the establishment and tearing down of calls) and an MG(a simple entity that responds to the MGC requests and independently processes media streams)

System Overview

An H.248 trunking gateway is a PSTN-IP telephony gateway. It interfaces with both the IP telephony network and the PSTN network by passing voice traffic from one network to the other. For the SS7 configuration, signaling bypasses the trunking gateway and directly terminates at the MGC.

Although H.248 is designed to be generic in its support for many different kinds of media, the PGW is mainly designed to act as an MGC and only interwork with trunking gateways. This feature addresses only the functionality of the interworking of the PGW with trunking gateways. Figure 1 shows an overview of this system.

Figure 1 H.248 Protocol in the SS7 Network

Benefits

The following are benefits of this feature:

•PGW supports H.248 communicating with media gateways.

•PGW supports H.248 capabilities and procedures as specified in H.248.1 Gateway control protocol: Version 2.

•PGW supports the use of H.248 and MGCP at the same time, that is, one gateway uses H.248 while another gateway uses MGCP. sigPath property GWProtocolVersion decides whether H.248 protocol or MGCP protocol is used.

Restrictions

The following are restrictions for this feature:

•The number of media gateways (MGs) that can be provisioned on one PGW depends on the platform capability.

•Up to two terminations can be included in one context, and at least one termination is a physical termination.

•PGW supports encoding and decoding of messages only in text format.

•PGW supports sending a message using only a short token.

•Each message can include only one transaction.

•PGW does not support a seamless upgrade from MGCP mode to H.248 mode on the same VXSM card.

Installation, Upgrade, and Fallback Procedures

Because the VXSM card does not support a seamless gateway upgrade from MGCP mode to H.248 mode on the same card, changing the operation mode on the same gateway can affect service. Follow these steps to change the mode.

PGW side:

1. Delete the current mgcppath and switchtrnk provisioned for this gateway.

2. Provision h248path and switchtrnk for this gateway.

VXSM side:

1. Clear the VXSM card's current configuration.

2. Configure it into H.248 mode, and various other configurations on the card.

After this, the gateway is ready to work under H.248 mode.

Related Documents

This document contains information that is related to this feature. The documents that contain additional information related to the Cisco Media Gateway Controller (MGC) are at

•cntxId—For sta-aud-h248:terms:sigpath can be ALL or a specified context ID. Use 0 to specify NULL context ID.

•cntxId—For sta-aud-h248:cntxs:sigpath can be specified context ID. ALL context ID or 0 context ID is not allowed.

•termId—Can be a specified termination ID or a wildcard. If you use a wildcard, termId can have, at most, one "*", for example, termId="DS/OC3_1/T1_1/*" is allowed, but termId="DS/OC3_1/*/*" is not allowed.

Example:

The MML command shown in the following example starts an audit on an H.248 gateway on sigpath H248-sigpath-01:

mml> sta-aud-h248:gateway:sigpath="h248-sigpath-01"

Comments:

Performance Impact Category: C.

Modified MML Commands

This section contains the MML commands that are modified for this feature.

Configures the H.248 transport protocol as UDP. There is a new parameter SVC that refers to H248PATH. This property uses sigChanDevIp.dat and sigChanDev.dat. The sessionset type in sigChanDevIp.dat could be used to indicate H248_UDP.

Software Changes for This Feature

Alarms

This section lists the alarms that are added and modified to support this feature. For information on the other alarms for the Cisco MGC software, see the Cisco Media Gateway Controller Software Release 9 Messages Reference Guide at

This property indicates whether bulk audit is supported on the associated gateway.

Valid values: boolean (1 = supported, 0 = not supported).

Default value: 1

Dynamically reconfigurable: yes

h248CongestionEnable

This property specifies whether a congestion control procedure is enabled for that GW.

Valid values: boolean. (0 = not enabled, 1 = enabled)

Default value: 0

Dynamically reconfigurable: yes

h248DomainNameRemote

This property specifies the default H.248 remote domain name. Use it to append to the audit command and send it to the remote gateway.

Value range: any valid domain name or NULL.

Valid values: string (up to 127 characters)

Default value: NULL

Dynamically reconfigurable: no

H248GatewayReserveValue

Note This property is deleted in Release 9.7P23 and later.

This property allows H.248 to send ADD commands with the ReserveValue "on" or "off" to indicate whether the MG should reverse resource or not. This property is applied only to the originating MG; for the terminating side, the ReserveValue is always "off".

Valid values: 0 or 1 (boolean)

where:

0 = do not reserve resource

1 = reserve resource

Default value: 0

Dynamically reconfigurable: yes

h248GWStdbyHeartbeatInterval

This property specifies the interval time, in seconds, that enables the MGC to send the heartbeat to complete a health check on the remote gateway using the standby IP link.

Valid values: integer (0 to 30 seconds)

Default value: 30

Dynamically reconfigurable: no

h248inactivitytimer

This property specifies an a value of an allowable period of silence in milliseconds.; the interval value must be no less than 1000.

This property specifies a poll count that defines the number of attempts to reach the remote GW for each configured local IP interface.

Valid values: integer (0 to 30)

Default value: 6

Dynamically reconfigurable: no

h248longtimer

This property indicates the H.248 long timer period.

Valid values: integer

Default value: 30

Dynamically reconfigurable: no

h248maxretries

This property indicates the maximum number of retransmissions to be done to the peer.

Valid values: integer (from 7 to 11)

Default value: 11

Dynamically reconfigurable: no

h248mgcexectimer

This property is used in calculating the normal MGC execution time (measured in milliseconds). This property specifies the interval at which the MGC sends a Transaction Pending message back to the MG if a transaction request on the MGC is pending.

Valid values: any integer

Default value: 500

Dynamically reconfigurable: no

h248mgexectimer

This property specifies the interval at which the MGC receives a response to any transaction from the MG. The network delay is excluded.

Valid values: any integer

Default value: 500

Dynamically reconfigurable: no

h248mgcpendlimit

This property indicates the number of transactions pending that can be received from the MGC.

Valid values: integer

Default value: 10

Dynamically reconfigurable: no

h248mgpendlimit

This property indicates the number of transactions pending that can be received from the MG.

Valid values: integer

Default value: 10

Dynamically reconfigurable: no

h248profilename

This property specifies the profile name that defines how the H.248.1 protocol is used and what functionality is supported by an MG. The profile itself specifies what options associated with H.248.1 have been used.

Valid values: string (up to 64 characters)

Default value: NULL

Dynamically reconfigurable: no

h248profileversion

This property specifies the H.248 profile version.

Valid values: integer (1 to 99)

Default value: 1

Dynamically reconfigurable: no

h248RemoteIpPollCount

This property specifies a poll count that defines the number of retry audit messages to be sent to the remote gateway.

Valid values: integer (0 to 30)

Default value: 72

Dynamically reconfigurable: no

h248TimerT1

This property specifies the interval at which the media gateway sends congestion notification to MGC if media gateway is still in congestion state. The unit is milliseconds.

Valid values: integer (0 to 100)

Default value: 0

Dynamically reconfigurable: yes

h248txnpendrespcount

This property indicates the number of pending transactions that can be received from the MG/MGC.

Valid values: integer

Default value: 11

Dynamically reconfigurable: no

h248mgcprovresptimer

This property is used in calculating the provisional response timer value (measured in milliseconds). It is initially set to normalMGCExecutionTime plus network delay, but it can be lowered.

Valid Values: any integer

Default Value: 600

Dynamically Reconfigurable: no

XECfgParm.dat Parameters

The XECfgParm.dat file configuration parameters added for this feature are in Table 2. For information on the other XECfgParm.dat parameters, see the Cisco Media Gateway Controller Software Release 9 Installation and Configuration Guide at

Included in the H.248 message from PGW to gateway. It can be an IP address in the format of X.X.X.X, or it can be a domain name.

maximumActionsInTransaction

Used to set the maximum number of actions in one H.248 Transaction.

maxNumH248Links

Maximum number of H.248 links for a PGW.

MgcHeaderAddrType

PGW H.248 local MID type, 1 for IP address and 2 for domain name.

Billing Interface

This section identifies the call detail record (CDR) data modified for this feature. For billing interface information for the rest of the Cisco MGC software, see the Cisco Media Gateway Controller Software Release 9 Billing Interface Guide at

Ingress Packet Information (Tag: 4046)

Tag 4046 contains the packets sent, packets received, packets lost, octets sent, octets received, jitter, and latency information (reserved 1 and 2) from the ingress gateway. For an H.248 call, the subfield definitions are unchanged and the data is filled with the statistics of Network Package (nt) and RTP Package (rtp) in H.248.

Egress Packet Information (Tag: 4047)

Tag 4047 contains the same information as Tag 4046 except that the data is taken from the egress gateway. The mapping is the same as with Tag 4046.

Ingress Protocol ID (Tag: 4069)

The ingress protocol ID is determined from MDL and is used in measurements and billing. New protocol type: "10 = H.248" is added to the definition.

Ingress MGCP DLCX Return Code (Tag: 4087)

Tag 4087 is an indication of MGCP DLCX (Delete Connection) return code value on the ingress gateway. If an H.248 gateway was engaged on the ingress side, this tag is not be logged in to CDR.

Egress MGCP DLCX Return Code (Tag: 4088)

Tag 4088 contains the same information as Tag 4087 except that the information comes from the egress gateway. For the H.248 gateway, this tag is not be logged in to CDR.

MGCP Script Response String (Tag: 4097)

For MGCP script hand-off calls, Tag 4097 records the Notification response string, if any, returned in the O parameter of the MGCP NTFY message. If this call did not receive an MGCP NTFY message, this tag is not logged. As MGCP scripting is not ported to H.248, H.248 calls never generate this CDB.

Originating Leg DSP Statistics (Tag: 4098)

Tag 4098 provides DSP statistics for the originating leg of the call. Because DSP statistics in CDR are not supported for H.248, this tag is not logged in to CDR for the H.248 leg.

Terminating Leg DSP Statistics (Tag: 4099)

Tag 4099 is the same as Tag 4098, except that it concerns the terminating leg.

Obtaining Documentation, Obtaining Support, and Security Guidelines

For information on obtaining documentation, obtaining support, providing documentation feedback, security guidelines, and also recommended aliases and general Cisco documents, see the monthly What's New in Cisco Product Documentation, which also lists all new and revised Cisco technical documentation at:

http://www.cisco.com/en/US/docs/general/whatsnew/whatsnew.html

Glossary

Table 3 contains expansions of acronyms and technical terms used in this feature module.

Table 3 Acronyms and Expansions

Acronym

Expansion

EISUP

Enhanced ISUP

GTD

Generic Transparency Descriptor

HSI

H.323 Signaling Interface

ISUP

ISDN User Part

MG

Media gateway

MGC

Media gateway controller

MGCP

Media Gateway Control Protocol

MML

Man-Machine Language

PGW

PSTN gateway

PSTN

Public Switched Telephony Network

RTT

Round-Trip Time

SDP

Session Description Protocol

SIP

Session Initiation Protocol

TGW

Trunking Gateway

TP

Terminal Portability

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